[SLIP]: Simplify sl_free_bufs()

We can avoid assignments to the local variable 'tmp' and 
actually get rid of tmp alltogether in sl_free_bufs(). This patch does 
that.  This is safe since both kfree() and slhc_free() handles NULL 
pointers gracefully.
Signed-off-by: NJesper Juhl <juhl-lkml@dif.dk>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/slip.c

@@ -198,18 +198,12 @@ sl_alloc_bufs(struct slip *sl, int mtu)
 static void
 sl_free_bufs(struct slip *sl)
 {
-	void * tmp;
-
 	/* Free all SLIP frame buffers. */
-	tmp = xchg(&sl->rbuff, NULL);
-	kfree(tmp);
-	tmp = xchg(&sl->xbuff, NULL);
-	kfree(tmp);
+	kfree(xchg(&sl->rbuff, NULL));
+	kfree(xchg(&sl->xbuff, NULL));
 #ifdef SL_INCLUDE_CSLIP
-	tmp = xchg(&sl->cbuff, NULL);
-	kfree(tmp);
-	if ((tmp = xchg(&sl->slcomp, NULL)) != NULL)
-		slhc_free(tmp);
+	kfree(xchg(&sl->cbuff, NULL));
+	slhc_free(xchg(&sl->slcomp, NULL));
 #endif
 }